Field of the Inventive Concepts
The inventive concepts disclosed herein pertain generally to the field of aircraft display units that present information to the pilot of an aircraft.
Description of the Related Art
A vertical descent path (VDP) of an aircraft's flight path is typically assigned a fixed vertical path angle (VPA). Perhaps the most common VPA is three degrees although this may differ due to, for instance, altitude constraints built into the VDP. When it comes time to fly the VDP, an aircraft system(s) may be configured (or programmed) to control the aircraft pitch so that the aircraft follows the VDP while maintaining a descent speed target through movement of the aircraft throttle(s). An autothrottle system may increase the speed of the aircraft by “adding throttle” (i.e., increasing engine thrust) and may decrease the speed by retarding the throttle without pilot intervention; however, the system may not decrease the throttle past a defined idle setting for the engines and, therefore may not reduce speed without pilot intervention of imparting “drag” through, for instance, the use of speed brakes if a speed brake system is installed. If the actual VDP path on which the aircraft is flying is too steep and the drag is insufficient, the system may not be able to maintain the descent speed. When the VPA is a fixed, three degree angle, the amount of throttle required to maintain the VDP is typically above idle. The excess fuel consumption—the amount of fuel needed to power the engines above idle—increases operating costs as fuel is wasted in light of the relatively large amount of total energy available to the aircraft during descent.
A flight idle descent (FID) path could be employed by utilizing predictive atmospheric conditions, and the physical performance of the aircraft may be employed by an algorithm(s) to determine an ideal descent path that may never require the aircraft's throttles to move above idle and never require pilot intervention to impart additional drag. The aircraft's available total energy comprised of available potential energy and kinetic energy may be exploited along the FID path such that the total energy expended equals the energy required to maintain the desired descent speed of the FID path. Performance factors such as, for example, the drag of the aircraft, the predicted temperatures and winds at points along the path, and weight of the aircraft may be used to create a FID path. The FID path may start from a Top of Descent (TOD) and end at approach start point (ASP) or a defined waypoint such as, for example, a final approach fix of an instrument approach procedure. If the FID path requires a change of speed, this is achieved simply by changing the VPA without having to adjust the throttles. Speed may be maintained through the descent by changing the VPA to manage the conversion of potential energy to kinetic energy without the use of throttles.
The TOD is the point if flight where, if the engine thrust is reduced to idle and/or continues to operate at idle, the aircraft decelerates throughout the approach while reducing fuel consumption and reaching flap/slat retraction speeds and/or final approach speed. Unlike the FID path, the ASP could be defined by a specific geometric, fixed-angle path that is not subjected to being altered, a determining factor in locating its start point.